Layered support material for catalysts

ABSTRACT

The present invention addresses at least four different aspects relating to catalyst structure, methods of making those catalysts and methods of using those catalysts for making alkenyl alkanoates. Separately or together in combination, the various aspects of the invention are directed at improving the production of alkenyl alkanoates and VA in particular, including reduction of by-products and improved production efficiency. A first aspect of the present invention pertains to a unique palladium/gold catalyst or pre-catalyst (optionally calcined) that includes rhodium or another metal. A second aspect pertains to a palladium/gold catalyst or pre-catalyst that is based on a layered support material where one layer of the support material is substantially free of catalytic components. A third aspect pertains to a palladium/gold catalyst or pre-catalyst on a zirconia containing support material. A fourth aspect pertains to a palladium/gold catalyst or pre-catalyst that is produced from substantially chloride free catalytic components.

CLAIM OF PRIORITY

The present application is a divisional of Ser. No. 10/993,507, filed onNov. 19, 2004, which claims the benefit of U.S. provisional applications60/531,415; 60/530,936; 60/531,486; and 60/530,937, all filed on Dec.19, 2003, all of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to catalysts, methods of making thecatalysts, and methods of making alkenyl alkanoates. More particularly,the invention relates to methods of making vinyl acetate.

BACKGROUND OF THE INVENTION

Certain alkenyl alkanoates, such as vinyl acetate (VA), are commoditychemicals in high demand in their monomer form. For example, VA is usedto make polyvinyl acetate (PVAc), which is used commonly for adhesives,and accounts for a large portion of VA use. Other uses for VA includedpolyvinyl alcohol (PVOH), ethylene vinyl acetate (EVA), vinyl acetateethylene (VAE), polyvinyl butyral (PVB), ethylene vinyl alcohol (EVOH),polyvinyl formal (PVF), and vinyl chloride-vinyl acetate copolymer. PVOHis typically used for textiles, films, adhesives, and photosensitivecoatings. Films and wire and cable insulation often employ EVA in someproportion. Major applications for vinyl chloride-vinyl acetatecopolymer include coatings, paints, and adhesives often employ VAEhaving VA in some proportion. VAE, which contains more than 50 percentVA, is primarily used as cement additives, paints, and adhesives. PVB ismainly used for under layer in laminated screens, coatings, and inks.EVOH is used for barrier films and engineering polymers. PVF is used forwire enamel and magnetic tape.

Because VA is the basis for so many commercially significant materialsand products, the demand for VA is large, and VA production isfrequently done on a relatively large scale, e.g. 50,000 metric tons ormore per year. This large scale production means that significanteconomies of scale are possible and relatively subtle changes in theprocess, process conditions or catalyst characteristics can have asignificant economic impact on the cost of the production of VA.

Many techniques have been reported for the production of alkenylalkanoates. For example, in making VA, a widely used technique includesa catalyzed gas phase reaction of ethylene with acetic acid and oxygen,as seen in the following reaction:

C₂H₄+CH₃COOH+0.5O₂→CH₃COOCH═CH₂+H₂O

Several side reactions may take place, including, such as, the formationof CO₂. The results of this reaction are discussed in terms of thespace-time yield (STY) of the reaction system, where the STY is thegrams of VA produced per liter of catalyst per hour of reaction time(g/l*h).

The composition of the starting material feed can be varied within widelimits. Typically, the starting material feed includes 30-70% ethylene,10-30% acetic acid and 4-16% oxygen. The feed may also include inertmaterials such as CO₂, nitrogen, methane, ethane, propane, argon and/orhelium. The primary restriction on feed composition is the oxygen levelin the effluent stream exiting the reactor must be sufficiently low suchthat the stream is outside the flammability zone. The oxygen level inthe effluent is affected by the oxygen level in the starting materialstream, O₂ conversion rate of the reaction and the amount of any inertmaterial in the effluent.

The gas phase reaction has been carried out where a feed of the startingmaterials is passed over or through fixed bed reactors. Successfulresults have been obtained through the use of reaction temperatures inthe range of −125° C. to 200° C., while reaction pressures of 1-15atmospheres are typical.

While these systems have provided adequate yields, there continues to bea need for reduced production of by-products, higher rates of VA output,and lower energy use during production. One approach is to improvecatalyst characteristics, particularly as to CO₂ selectivity and/oractivity of the catalyst. Another approach is to modify reactionconditions, such as the ratio of starting materials to each other, theO₂ conversion of the reaction, the space velocity (SV) of the startingmaterial feed, and operating temperatures and pressures.

The formation of CO₂ is one aspect which may be reduced through the useof improved catalysts. The CO₂ selectivity is the percentage of theethylene converted that goes to CO₂. Decreasing the CO₂ selectivitypermits a larger amount of VA per unit volume and unit time in existingplants, even retaining all other reaction conditions.

VA output of a particular reaction system is affected by several otherfactors including the activity of the catalyst, the ratio of startingmaterials to each other, the O₂ conversion of the reaction, the spacevelocity (SV) of the starting material feed, and operating temperaturesand pressures. All these factors cooperate to determine the space-timeyield (STY) of the reaction system, where the STY is discussed in termsof grams of VA produced per liter of catalyst per hour of reaction timeor g/l*h.

Generally, activity is a significant factor in determining the STY, butother factors may still have a significant impact on the STY. Typically,the higher the activity of a catalyst, the higher the STY the catalystis able to produce.

The O2 conversion is a measure of how much oxygen reacts in the presenceof the catalyst. The O₂ conversion rate is temperature dependent suchthat the conversion rate generally climbs with the reaction temperature.However, the amount of CO₂ produced also increases along with the O₂conversion. Thus, the O₂ conversion rate is selected to give the desiredVA output balanced against the amount of CO₂ produced. A catalyst with ahigher activity means that the overall reaction temperature can belowered while maintaining the same O₂ conversion. Alternatively, acatalyst with a higher activity will give a higher O₂ conversion rate ata given temperature and space velocity.

It is common that catalysts employ one or more catalytic componentscarried on a relatively inert support material. In the case of VAcatalysts, the catalytic components are typically a mixture of metalsthat may be distributed uniformly throughout the support material (“allthrough-out catalysts”), just on the surface of the support material(“shell catalysts”), just below a shell of support material (“egg whitecatalysts”) or in the core of the support material (“egg yolkcatalysts”).

Numerous different types of support materials have been suggested foruse in VA catalyst including silica, cerium doped silica, alumina,titania, zirconia and oxide mixtures. But very little investigation ofthe differences between the support materials has been done. For themost part, only silica and alumina have actually been commercialized assupport materials.

One useful combination of metals for VA catalysis is palladium and gold.Pd/Au catalysts provide adequate CO₂ selectivity and activity, but therecontinues to be a need for improved catalysts given the economies ofscale that are possible in the production of VA.

One process for making Pd/Au catalysts typically includes the steps ofimpregnating the support with aqueous solutions of water-soluble saltsof palladium and gold; reacting the impregnated water-soluble salts withan appropriate alkaline compound e.g., sodium hydroxide, to precipitate(often called fixing) the metallic elements as water-insolublecompounds, e.g. the hydroxides; washing the fixed support material toremove un-fixed compounds and to otherwise cleanse the catalyst of anypotential poisons, e.g. chloride; reducing the water insoluble compoundswith a typical reductant such as hydrogen, ethylene or hydrazine, andadding an alkali metal compound such as potassium or sodium acetate.

Various modifications to this basic process have been suggested. Forexample, in U.S. Pat. No. 5,990,344, it is suggested that sintering ofthe palladium be undertaken after the reduction to its free metal form.In U.S. Pat. No. 6,022,823, it suggested that calcining the support in anon-reducing atmosphere after impregnation with both palladium and goldsalts might be advantageous. In WO94/21374, it is suggested that afterreduction and activation, but before its first use, the catalyst may bepretreated by successive heating in oxidizing, inert, and reducingatmospheres.

In U.S. Pat. No. 5,466,652, it is suggested that salts of palladium andgold that are hydroxyl-, halide- and barium-free and soluble in aceticacid may be useful to impregnate the support material. A similarsuggestion is made in U.S. Pat. No. 4,902,823, i.e. use of halide- andsulfur-free salts and complexes of palladium soluble in unsubstitutedcarboxylic acids having two to ten carbons.

In U.S. Pat. No. 6,486,370, it suggested that a layered catalyst may beused in a dehydrogenation process where the inner layer support materialdiffers from the outer layer support material. Similarly, U.S. Pat. No.5,935,889 suggests that a layered catalyst may useful as acid catalysts.But neither suggests the use of layered catalysts in the production ofalkenyl alkanoates.

Taken together, the inventors have recognized and addressed the need forcontinued improvements in the field of VA catalysts to provide improvedVA production at lower costs.

SUMMARY OF THE INVENTION

The present invention addresses at least four different aspects relatingto catalyst structure, methods of making those catalysts and methods ofusing those catalysts for making alkenyl alkanoates. Separately ortogether in combination, the various aspects of the invention aredirected at improving the production of alkenyl alkanoates and VA inparticular, including reduction of by-products and improved productionefficiency. A first aspect of the present invention pertains to a uniquepalladium/gold catalyst or pre-catalyst (optionally calcined) thatincludes rhodium or another metal. A second aspect pertains to apalladium/gold catalyst or pre-catalyst that is based on a layeredsupport material where one layer of the support material issubstantially free of catalytic components. A third aspect pertains to apalladium/gold catalyst or pre-catalyst on a zirconia containing supportmaterial. A fourth aspect pertains to a palladium/gold catalyst orpre-catalyst that is produced from substantially chloride free catalyticcomponents.

DETAILED DESCRIPTION

Catalysts

For present purposes, a catalyst is any support material that containsat least one catalytic component and that is capable of catalyzing areaction, whereas a pre-catalyst is any material that results from anyof the catalyst preparation steps discussed herein.

Catalysts and pre-catalysts of the present invention may include thosehaving at least one of the following attributes: 1) the catalyst will bea palladium and gold containing catalyst that includes at least anothercatalytic component, e.g. rhodium where the one or more of the catalyticcomponents have been calcined; 2) the catalyst will be carried on alayered support, 3) the catalyst will be carried on a zirconiacontaining support material; 4) the catalyst will be produced withchloride free precursors or any combination of the foregoing. Effectiveuse of the catalyst accordingly should help improve CO₂ selectivity,activity or both, particularly as pertaining to VA production.

It should be appreciated that the present invention is described in thecontext of certain illustrative embodiments, but may be varied in any ofa number of aspects depending on the needs of a particular application.By way of example, without limitation, the catalysts may have thecatalytic components uniformly distributed throughout the supportmaterial or they may be shell catalysts where the catalytic componentsare found in a relatively thin shell around a support material core. Eggwhite catalysts may also be suitable, where the catalytic componentsreside substantially away from the center of support material. Egg yolkcatalysts may also be suitable.

Catalytic Components

In general, the catalysts and pre-catalysts of the present inventioninclude metals and particularly include a combination of at least twometals. In particular, the combination of metals includes at least onefrom Group VIIIB and at least one from Group IB. It will be appreciatedthat “catalytic component” is used to signify the metal that ultimatelyprovides catalytic functionally to the catalyst, but also includes themetal in a variety of states, such as salt, solution, sol-gel,suspensions, colloidal suspensions, free metal, alloy, or combinationsthereof. Preferred catalysts include palladium and gold as the catalyticcomponents.

One embodiment of the catalyst includes a combination of catalyticcomponents having palladium and gold combined with a third catalyticcomponent. The third catalytic component is preferably selected fromGroup VIIIB, with Rh being the most preferred. Other preferred catalystsinclude those where the third catalytic component is selected from W,Ni, Nb, Ta, Ti, Zr, Y, Re, Os, Fe, Cu, Co, Zn, In, Sn, Ce, Ge, Ga andcombinations thereof.

Another embodiment of the catalyst includes a combination of catalyticcomponents including proportions of palladium, gold, and rhodium.Optionally a third catalytic component (as listed above) may also beincluded in this embodiment in place of Rh. In another embodiment, twoor more catalytic components from the above list may be employed.

In one example, palladium and gold may be combined with Rh to form acatalyst that shows improved CO₂ selectively (i.e. decreased formationof CO₂) compared to Pd/Au catalysts that lack Rh. Also, the addition ofRh does not appear to adversely affect the activity of the catalyst. TheCO₂ selectivity of the palladium, gold, rhodium catalyst may also beimproved through calcining during the catalyst preparation and/orthrough the use of water-soluble halide free precursors (both discussedbelow), although these are not necessary to observe the Rh effect

The atomic ratio of the third catalytic component to palladium may be inthe range of about 0.005 to about 1.0, more preferably about 0.01 toabout 1.0. In one embodiment, the catalyst contains between about 0.01and about 5.0 g of the third catalytic component per liter of catalyst.

Another preferred embodiment of the catalyst includes between about 1 toabout 10 grams of palladium, and about 0.5 to about 10 grams of gold perliter of catalyst. The amount of gold is preferably from about 10 toabout 125 wt % based on the weight of palladium.

In one embodiment for ground catalysts, Au to Pd atomic ratios betweenabout 0.5 and about 1.00 may be preferred for ground catalysts. Theatomic ratio can be adjusted to balance the activity and CO₂selectivity. Employment of higher Au/Pd weight or atomic ratios tends tofavor more active, more selective catalysts. Stated alternatively, acatalyst with an atomic ratio of about 0.6 is less selective for CO₂,but also has less activity than a catalyst with a ratio of about 0.8.The effect of the high Au/Pd atomic ratio on ground support material mayalso be enhanced through the use of relatively high excess of hydroxideion, as discussed below with respect to the fixing step. A groundcatalyst may be one where the catalytic components are contacted to thesupport material followed by a reduction in the particle size (e.g. bygrinding or ball milling) or one where the catalytic components arecontacted to the support material after the support material has beenreduced in size.

For shell catalysts, the thickness of the shell of catalytic componentson the support material ranges from about 5 Mm to about 500 Mm. Morepreferred ranges include from about 5 Mm to about 300 Mm.

Support Materials

As indicated, in one aspect of the invention, the catalytic componentsof the present invention generally will be carried by a supportmaterial. Suitable support materials typically include materials thatare substantially uniform in identity or a mixture of materials.Overall, the support materials are typically inert in the reaction beingperformed. Support materials may be composed of any suitable substancepreferably selected so that the support materials have a relatively highsurface area per unit mass or volume, such as a porous structure, amolecular sieve structure, a honeycomb structure, or other suitablestructure. For example, the support material may contain silica,alumina, silica-alumina, titania, zirconia, niobia, silicates,aluminosilicates, titanates, spinel, silicon carbide, silicon nitride,carbon, cordierite, steatite, bentonite, clays, metals, glasses, quartz,pumice, zeolites, non-zeolitic molecular sieves combinations thereof andthe like. Any of the different crystalline form of the materials mayalso be suitable, e.g. alpha or gamma alumina. Silica and zirconiacontaining support materials are the most preferred. In addition,multilayer support materials are also suitable for use in the presentinvention.

The support material in the catalyst of this invention may be composedof particles having any of various regular or irregular shapes, such asspheres, tablets, cylinders, discs, rings, stars, or other shapes. Thesupport material may have dimensions such as diameter, length or widthof about 1 to about 10 mm, preferably about 3 to about 9 mm. Inparticular having a regular shape (e.g. spherical) will have as itspreferred largest dimension of about 4 mm to about 8 mm. In addition, aground or powder support material may be suitable such that the supportmaterial has a regular or irregular shape with a diameter of betweenabout 10 microns and about 1000 micron, with preferred sizes beingbetween about 10 and about 700 microns, with most preferred sizes beingbetween about 180 microns and about 450 microns. Larger or smaller sizesmay be employed, as well as polydisperse collections of particles sizes.For example, for a fluid bed catalyst a preferred size range wouldinclude 10 to 150 microns. For precursors used in layered catalysts, asize range of 10 to 250 microns is preferred.

Surface areas available for supporting catalytic components, as measuredby the BET (Brunauer, Emmett, and Teller) method, may generally bebetween about 1 m²/g and about 500 m²/g, preferably about 100 m²/g toabout 200 m²/g. For example, for a porous support, the pore volume ofthe support material may generally be about 0.1 to about 2 ml/g, andpreferably about 0.4 to about 1.2 ml/g. An average pore size in therange, for example, of about 50 to about 2000 angstroms is desirable,but not required.

Examples of suitable silica containing support materials include KA160from Sud Chemie, Aerolyst350 from Degussa and other pyrogenic ormicroporous-free silicas with a particle size of about 1 mm to about 10mm.

Examples of suitable zirconia containing support materials include thosefrom N or Pro, Zirconia Sales (America), Inc., Daichi Kigenso KagakuKogyo, and Magnesium Elektron Inc (MEI). Suitable zirconia supportmaterials have a wide range of surface areas from less than about 5 m²/gto more than 300 m²/g. Preferred zirconia support materials have surfaceareas from about 10 m²/g to about 135 m²/g. Support materials may havetheir surfaces treated through a calcining step in which the virginsupport material is heated. The heating reduces the surface area of thesupport material (e.g. calcining). This provides a method of creatingsupport materials with specific surface areas that may not otherwise bereadily available from suppliers.

In another embodiment, it is contemplated to employ at least a pluralcombination of support materials, each with a different characteristic.For example, at least two support materials (e.g. zirconia) withdifferent characteristics may exhibit different activities and CO₂selectivities, thus permitting preparation of catalysts with a desiredset of characteristics, i.e. activity of a catalyst may be balancedagainst the CO₂ selectivity of the catalyst.

In one embodiment, plural different supports are employed in a layeredconfiguration. Layering may be achieved in any of a number of differentapproaches, such as a plurality of lamella that are generally flat,undulated or a combination thereof. One particular approach is toutilize successively enveloping layers relative to an initial corelayer. In general, herein, layered support materials typically includeat least an inner layer and an outer layer at least partiallysurrounding the inner layer. The outer layer preferably containssubstantially more of catalytic components than the inner layer. In oneembodiment, the inner and outer layers are made of different materials;but the materials may be the same. While the inner layer may benon-porous, other embodiments include an inner layer that is porous.

The layered support material preferably results in a form of a shellcatalyst. But the layered support material offers a well definedboundary between the areas of the support material that have catalyticcomponents and the areas that do not. Also, the outer layer can beconstructed consistently with a desired thickness. Together the boundaryand the uniform thickness of the outer layer result in a shell catalystthat is a shell of catalytic components that is of a uniform and knownthickness.

Several techniques are known for creating layered support materialsincludes those described in U.S. Pat. Nos. 6,486,370; 5,935,889; and5,200,382, each of which is incorporated by reference. In oneembodiment, the materials of the inner layer are also not substantiallypenetrated by liquids, e.g., metals including but not limited toaluminum, titanium and zirconium. Examples of other materials for theinner layer include, but are not limited to, alumina, silica,silica-alumina, titania, zirconia, niobia, silicates, aluminosilicates,titanates, spinel, silicon carbide, silicon nitride, carbon, cordierite,steatite, bentonite, clays, metals, glasses, quartz, pumice, zeolites,non-zeolitic molecular sieves and combinations thereof. A preferredinner layer is silica and KA160, in particular.

These materials which make up the inner layer may be in a variety offorms such as regularly shaped particulates, irregularly shapedparticulates, pellets, discs, rings, stars, wagon wheels, honeycombs orother shaped bodies. A spherical particulate inner layer is preferred.The inner layer, whether spherical or not, has an effective diameter ofabout 0.02 mm to about 10.0 mm and preferably from about 0.04 mm toabout 8.0 mm.

The outermost layer of any multilayer structure is one which is porous,has a surface area in the range of about 5 m²/g to about 300 m²/g. Thematerial of the outer layer is a metal, ceramic, or a combinationthereof, and in one embodiment it is selected from alumina, silica,silica-alumina, titania, zirconia, niobia, silicates, aluminosilicates,titanates, spinel, silicon carbide, silicon nitride, carbon, cordierite,steatite, bentonite, clays, metals, glasses, quartz, pumice, zeolites,non-zeolitic molecular sieves and combinations thereof and preferablyinclude alumina, silica, silica/alumina, zeolites, non-zeolite molecularsieves (NZMS), titania, zirconia and mixtures thereof. Specific examplesinclude zirconia, silica and alumina or combinations thereof.

While the outer layer typically surrounds substantially the entire innerlayer, this is not necessarily the case and a selective coating on theinner layer by the outer layer may be employed.

The outer layer may be coated on to the underlying layer in a suitablemanner. In one embodiment, a slurry of the outer layer material isemployed. Coating of the inner layer with the slurry may be accomplishedby methods such as rolling, dipping, spraying, wash coating, otherslurry coating techniques, combinations thereof or the like. Onepreferred technique involves using a fixed or fluidized bed of innerlayer particles and spraying the slurry into the bed to coat theparticles evenly. The slurry may be applied repeatedly in small amounts,with intervening drying, to provide an outer layer that is highlyuniform in thickness.

The slurry utilized to coat the inner layer may also include any of anumber of additives such as a surfactant, an organic or inorganicbonding agent that aids in the adhesion of the outer layer to anunderlying layer, or combinations thereof. Examples of this organicbonding agent include but are not limited to PVA,hydroxypropylcellulose, methyl cellulose, and carboxymethylcellulose.The amount of organic bonding agent which is added to the slurry mayvary, such as from about 1 wt % to about 15 wt % of the combination ofouter layer and the bonding agent. Examples of inorganic bonding agentsare selected from an alumina bonding agent (e.g. Bohmite), a silicabonding agent (e.g. Ludox, Teos), zirconia bonding agent (e.g. zirconiaacetate or colloidal zirconia) or combinations thereof. Examples ofsilica bonding agents include silica sol and silica gel, while examplesof alumina bonding agents include alumina sol, bentonite, Bohmite, andaluminum nitrate. The amount of inorganic bonding agent may range fromabout 2 wt % to about 15 wt % of the combination of the outer layer andthe bonding agent. The thickness of the outer layer may range from about5 microns to about 500 microns and preferably between about 20 micronsand about 250 microns.

Once the inner layer is coated with the outer layer, the resultantlayered support will be dried, such as by heating at a temperature ofabout 100° C. to about 320° C. (e.g. for a time of about 1 to about 24hours) and then may optionally be calcined at a temperature of about300° C. to about 900° C. (e.g. for a time of about 0.5 to about 10hours) to enhance bonding the outer layer to it underlying layer over aleast a portion of its surface and provide a layered catalyst support.The drying and calcining steps can be combined into one step. Theresultant layered support material may be contacted with catalyticcomponents just as any other support material in the production ofcatalysts, as described below. Alternately, the outer layer supportmaterial is contacted to catalytic components before it is coated ontothe underlying layer.

In another embodiment of the layered support, a second outer layer isadded to surround the initial outer layer to form at least three layers.The material for the second outer layer may be the same or differentthan the first outer layer. Suitable materials include those discussedwith respect to the first outer layer. The method for applying thesecond outer layer may be the same or different than the method used toapply the middle layer and suitable methods include those discussed withrespect to the first outer layer. Organic or inorganic bonding agents asdescribed may suitably used in the formation of the second outer layer.

The initial outer layer may or may not contain catalytic components.Similarly, the second outer layer may or may not contain catalyticcomponents. If both outer layers contain catalytic component, thenpreferably different catalytic components are used in each layer,although this is not necessarily the case. In one preferred embodiment,the initial outer layer does not contain a catalytic component.Contacting catalytic component to the outer layers may be accomplishedby impregnation or spray coating, as described below.

In embodiments where the initial outer layer contains catalyticcomponent, one method of achieving this is to contact the catalyticcomponent to the material of the initial outer layer before the materialis applied to the inner layer. The second outer layer may be applied tothe initial outer layer neat or containing catalytic component.

Other suitable techniques may be used to achieve a three layered supportmaterial in which one or more of the outer layers contain catalyticcomponents. Indeed, the layered support material is not limited to threelayers, but may include four, five or more layers, some or all of whichmay contain catalytic components.

In addition, the number and type of catalytic components that varybetween the layers of the layered support material, othercharacteristics (e.g. porosity, particle size, surface area, porevolume, or the like) of the support material may vary between thelayers.

Methods of Making Catalysts

In general the method includes contacting support material catalyticcomponents and reducing the catalytic components. Preferred methods ofthe present invention include impregnating the catalytic components intothe support material, calcining the catalytic component containingsupport material, reducing the catalytic components and modifying thereduced catalytic components on the support material. Additional stepssuch as fixing the catalytic components on the support material andwashing the fixed catalytic components may also be included in themethod of making the catalyst or pre-catalyst. Some of the steps listedabove are optional and others may be eliminated (e.g. the washingand/fixing steps). In addition, some steps may be repeated (e.g.multiple impregnation or fix steps) and the order of the steps may bedifferent from that listed above (e.g. the reducing step precedes thecalcining step). To a certain extent, the contacting step will determinewhat later steps are needed for the formation of the catalyst.

Contacting Step

One particular approach to contacting is one pursuant to which an eggyolk catalyst or pre-catalyst is formed, an egg white catalyst orpre-catalyst is formed, an all throughout catalyst or pre-catalyst isformed or a shell catalyst or pre-catalyst is formed, or a combinationthereof. In one embodiment, techniques that form shell catalysts arepreferred.

The contacting step may be carried out using any of the supportmaterials described above, with silica, zirconia and layered supportmaterials containing zirconia being the most favored. The contactingstep is preferably carried out at ambient temperature and pressureconditions; however, reduced or elevated temperatures or pressures maybe employed.

In one preferred contacting step, a support material is impregnated withone or more aqueous solutions of the catalytic components (referred toas precursor solutions). The physical state of the support materialduring the contacting step may be a dry solid, a slurry, a sol-gel, acolloidal suspension or the like.

In one embodiment, the catalytic components contained in the precursorsolution are water soluble salts made of the catalytic components,including but not limited to, chlorides, other halides, nitrates,nitrites, hydroxides, oxides, oxalates, acetates (OAc), and amines, withhalide free salts being preferred and chloride free salts being morepreferred. Examples of palladium salts suitable for use in precursorsolutions include PdCl₂, Na₂PdCl₄, Pd(NH₃)₂(NO₂)₂, Pd(NH₃)₄(OH)₂,Pd(NH₃)₄(NO₃)₂, Pd(NO₃)₂, Pd(NH₃)₄(OAc)₂, Pd(NH₃)₂(OAc)₂, Pd(OAc)₂ inKOH and/or NMe₄OH and/or NaOH, Pd(NH₃)₄(HCO₃)₂ and palladium oxalate. Ofthe chloride-containing palladium precursors, Na₂PdCl₄ is mostpreferred. Of the chloride free palladium precursor salts, the followingfour are the most preferred: Pd(NH₃)₄(NO₃)₂, Pd(NO₃)₂, Pd(NH₃)₂(NO₂)₂,Pd(NH₃)₄(OH)₂. Examples of gold salts suitable for use in precursorsolution include AuCl₃, HAuCl₄, NaAuCl₄, KAuO₂, NaAuO₂, NMe₄AuO₂,Au(OAc)₃ in KOH and/or NMe₄OH as well as HAu(NO₃)₄ in nitric acid, withKAuO₂ being the most preferred of the chloride free gold precursors.Examples of rhodium salts suitable for use in precursor solutionsinclude RhCl₃, Rh(OAc)₃, and Rh(NO₃)₂. Similar salts of the abovedescribed third catalytic components may also be selected.

Furthermore, more than one salt may be used in a given precursorsolution. For example, a palladium salt may be combined with a gold saltor two different palladium salts may be combined together in a singleprecursor solution. Precursor solutions typically may be made bydissolving the selected salt or salts in water, with or withoutsolubility modifiers such as acids, bases or other solvents. Othernon-aqueous solvents may also be suitable.

The precursor solutions may be impregnated onto the support materialsimultaneously (e.g. co-impregnation) or sequentially and may beimpregnated through the use of one or multiple precursor solutions. Withthree or more catalytic components, a combination of simultaneous andsequential impregnation may be used. For example, palladium and rhodiummay be impregnated through the use of a single precursor solution(referred to as a co-impregnation), followed by impregnation with aprecursor solution of the gold. In addition, a catalytic component maybe impregnated on to support material in multiple steps, such that aportion of the catalytic component is contacted each time. For example,one suitable protocol may include impregnating with Pd, followed byimpregnating with Au, followed by impregnating again with Au.

The order of impregnating the support material with the precursorsolutions is not critical; although there may be some advantages tocertain orders, as discussed below, with respect to the calcining step.Preferably, the palladium catalytic component is impregnated onto thesupport material first, with gold being impregnated after palladium, orlast. Rhodium or other third catalytic component, when used, may beimpregnated with the palladium, with the gold or by itself. Also, thesupport material may be impregnated multiple times with the samecatalytic component. For example, a portion of the overall goldcontained in the catalyst may be first contacted, followed by contactingof a second portion of the gold. One more other steps may intervenebetween the steps in which gold is contacted to the support material,e.g. calcining, reducing, and/or fixing.

The acid-base profile of the precursor solutions may influence whether aco-impregnation or a sequential impregnation is utilized. Thus, onlyprecursor solutions with similar acid-base profile should be usedtogether in a co-impregnating step; this eliminates any acid-basereactions that may foul the precursor solutions.

For the impregnating step, the volume of precursor solution is selectedso that it corresponds to between about 85% and about 110% of the porevolume of the support material. Volumes between about 95% and about 100%of the pore volume of the support material are preferred, and morepreferably between about 98% and about 99% of the pore volume.

Typically, the precursor solution is added to the support material andthe support material is allowed absorb the precursor solution. This maybe done drop wise until incipient wetness of the support material issubstantially achieved. Alternatively, the support material may beplaced by aliquots or batch wise into the precursor solution. Aroto-immersion or other assistive apparatus may be used to achievethorough contact between the support material and the precursorsolution. Further, a spray device may be used such that the precursorsolution is sprayed through a nozzle onto the support material, where itabsorbed. Optionally, decanting, heat or reduced pressure may be used toremove any excess liquid not absorbed by the support material or to drythe support material after impregnation.

For the impregnating step, the volume of precursor solution is selectedso that it corresponds to between about 85% and about 110% of the porevolume of the support material. Volumes between about 95% and about 100%of the pore volume of the support material are preferred, and morepreferably between about 98% and about 99% of the pore volume.

Typically, the precursor solution is added to the support material andthe support material is allowed absorb the precursor solution. This maybe done drop wise until incipient wetness of the support material issubstantially achieved. Alternatively, the support material may beplaced by aliquots or batch wise into the precursor solution. Aroto-immersion or other assistive apparatus may be used to achievethorough contact between the support material and the precursorsolution. Further, a spray device may be used such that the precursorsolution is sprayed through a nozzle onto the support material, where itabsorbed. Optionally, decanting, heat or reduced pressure may be used toremove any excess liquid not absorbed by the support material or to drythe support material after impregnation.

Other contacting techniques may be used to avoid a fixing step whilestill achieving a shell catalyst. For example, catalytic components maybe contacted to a support material through a chemical vapor depositionprocess, such as described in US2001/0048970, which is incorporated byreference. Also, spray coating or otherwise layering a uniformlypre-impregnated support material, as an outer layer, on to an innerlayer effectively forms shell catalyst that may also be described as alayered support material. In another technique, organometallicprecursors of catalytic components, particularly with respect to gold,may be used to form shell catalysts, as described in U.S. Pat. No.5,700,753, which is incorporated by reference.

A physical shell formation technique may also be suitable for theproduction of shell catalysts. Here, the precursor solution may besprayed onto a heated support material or a layered support material,where the solvent of the precursor solution evaporates upon contact withthe heated support material, thus depositing the catalytic components ina shell on the support material. Preferably, temperatures between about40 and 140° C. may be used. The thickness of the shell may be controlledby selecting the temperature of the support material and the flow rateof the solution through the spray nozzle. For example, with temperaturesabove about 100° C., a relatively thin shell is formed. This embodimentmay be particularly useful when chloride free precursors are utilized tohelp enhance the shell formation on the support material.

One skilled in the art will understand that a combination of thecontacting steps may be an appropriate method of forming a contactedsupport material.

Fixing Step

It may be desirable to transform at least a portion of the catalyticcomponents on the contacted support material from a water-soluble formto a water-insoluble form. Such a step may be referred to as a fixingstep. This may be accomplished by applying a fixing agent (e.g.dispersion in a liquid, such as a solution) to the impregnated supportmaterial which causes at least a portion of the catalytic components toprecipitate. This fixing step helps to form a shell catalyst, but is notrequired to form shell catalysts.

Any suitable fixing agent may be used, with hydroxides (e.g. alkalimetal hydroxides), silicates, borates, carbonates and bicarbonates inaqueous solutions being preferred. The preferred fixing agent is NaOH.Fixing may be accomplished by adding the fixing agent to the supportmaterial before, during or after the precursor solutions are impregnatedon the support material. Typically, the fixing agent is used subsequentto the contacting step such that the contacted support material isallowed to soak in the fixing agent solution for about 1 to about 24hours. The specific time depends upon the combination of the precursorsolution and the fixing agent. Like the impregnating step, an assistivedevice, such as a roto immersion apparatus as described in U.S. Pat. No.5,332,710, which is incorporated herein by reference, may advantageouslybe used in the fixing step.

The fixing step may be accomplished in one or multiple steps, referredas a co-fix or a separate fix. In a co-fix, one or more volumes of afixing agent solution is applied to the contacted support material afterall the relevant precursor solutions have been contacted to the supportmaterial, whether the contact was accomplished through the use of one ormultiple precursor solutions. For example, fixing after sequentialimpregnation with a palladium precursor solution, a gold precursorsolution and a rhodium precursor solution would be a co-fix, as wouldfixing after a co-impregnation with a palladium/rhodium precursorsolution followed by impregnation with a gold precursor solution. Anexample of co-fixing may be found in U.S. Pat. No. 5,314,888, which isincorporated by reference.

A separate fix, on the other hand, would include applying a fixing agentsolution during or after each impregnation with a precursor solution.For example, the following protocols would be a separate fix: a)impregnating palladium followed by fixing followed by impregnating withgold followed by fixing; or b) co-impregnating with palladium andrhodium followed by fixing followed by impregnating with gold followedby fixing. Between a fix and subsequent impregnation, any excess liquidmay be removed and the support material dried, although this is notnecessarily the case. An example of separate fixing may be found in U.S.Pat. No. 6,034,030, which is incorporated by reference.

In another embodiment, the fixing step and the contacting step areconducted simultaneously, one example of which is described in U.S. Pat.No. 4,048,096, which is incorporated by reference. For example, asimultaneous fix might be: impregnating with palladium followed byfixing followed by impregnating with gold and fixing agent. In avariation on this embodiment, the fix may be conducted twice for acatalytic component. A catalytic component may be partially fixed whenit is contacted to the support material (called a “pre-fix”), followedan additional, final fix. For example: impregnating with palladiumfollowed by impregnating with gold and a pre-fixing agent followed byfixing with a final fixing agent. This technique may be used to helpinsure the formation of shell type catalyst as opposed to an allthroughout catalyst.

In another embodiment, particularly suitable for use with chloride freeprecursors, the support material is pre-treated with a fixing agent toadjust the properties of the support material. In this embodiment, thesupport material is first impregnated with either an acid or basesolution, typically free of metals. After drying, the support materialis impregnated with a precursor solution that has the oppositeacidity/alkalinity as the dried support material. The ensuing acid-basereaction forms a shell of catalytic components on the support material.For example, nitric acid may be used to pre-treat a support materialthat in turn is impregnated with a basic precursor solution such asPd(OH)₂ or Au(OH)₃. This formation technique may be considered as usinga fixing step followed by a contacting step.

The concentration of fixing agent in the solution is typically a molarexcess of the amount of catalytic components impregnated on the supportmaterial. The amount of fixing agent should be between about 1.0 toabout 2.0, preferably about 1.1 to about 1.8 times the amount necessaryto react with the catalytically active cations present in thewater-soluble salt. In one embodiment using a high Au/Pd atomic orweight ratio, an increased molar excess of hydroxide ion enhances theCO₂ selectivity and activity of the resultant catalyst.

The volume of fixing agent solution supplied generally should be anamount sufficient to cover the available free surfaces of theimpregnated support material This may be accomplished by introducing,for example, a volume that is greater than the pore volume of thecontacted support material.

The combination of impregnating and fixing steps can form a shell typecatalyst. But, the use of halide free precursor solutions also permitsthe formation of a shell catalyst while optionally eliminating thefixing step. In the absence of a chloride precursor, a washing step, asdiscussed below, may be obviated. Further, the process can be free of astep of fixing catalytic components that would otherwise be needed tosurvive the washing step. Because no washing step is needed, thecatalytic components need not be fixed to survive the washing step.Subsequent steps in the method making the catalyst do not require thecatalytic components be fixed and thus the remainder of the step maybecarried out without additional preparatory steps. Overall, the use ofchloride free precursors permits a catalyst or pre-catalyst productionmethod that is free of a step of washing, thus reducing the number ofsteps needed to produce the catalyst and eliminating the need to disposeof chloride containing waste.

Washing Step

Particularly, when halide containing precursor solutions are utilizedand in other applications as desired, after the fixing step, the fixedsupport material may be washed to remove any halide residue on thesupport or otherwise treated to eliminate the potential negative effectof a contaminant on the support material. The washing step includedrinsing the fixed support material in water, preferably deionized water.Washing may be done in a batch or a continuous mode. Washing at roomtemperature should continue until the effluent wash water has a halideion content of less than about 1000 ppm, and more preferably until thefinal effluent gives a negative result to a silver nitrate test. Thewashing step may be carried out after or simultaneously with thereducing step, discussed below, but preferably is carried out before. Asdiscussed above, the use of halide free precursor solutions permits theelimination of the washing step.

Calcining Step

After at least one catalytic component has been contacted to the supportmaterial, a calcining step may be employed. The calcining step typicallyis before the reducing step and after the fixing step (if such a step isused) but may take place elsewhere in the process. In anotherembodiment, the calcining step is carried out after the reducing step.The calcining step includes heating the support material in anon-reducing atmosphere (i.e. oxidizing or inert). During calcination,the catalytic components on the support material are at least partiallydecomposed from their salts to a mixture of their oxide and free metalform.

For example, the calcining step is carried out at a temperature in therange of about 100° C. to about 700° C., preferably between about 200°C. and about 500° C. Non-reducing gases used for the calcination mayincluded one or more inert or oxidizing gases such as helium, nitrogen,argon, neon, nitrogen oxides, oxygen, air, carbon dioxide, combinationsthereof or the like. In one embodiment, the calcining step is carriedout in an atmosphere of substantially pure nitrogen, oxygen, air orcombinations thereof. Calcination times may vary but preferably arebetween about 1 and 5 hours. The degree of decomposition of thecatalytic component salts depends on the temperature used and length oftime the impregnated catalyst is calcined and can be followed bymonitoring volatile decomposition products.

One or more calcining steps may be used, such that at any point after atleast one catalytic component is contacted to the support material, itmay be calcined. Preferably, the last calcining step occurs beforecontact of the gold catalytic component to a zirconia support material.Alternately, calcining of a zirconia support material containing gold isconducted at temperatures below about 300° C. By avoiding calcining thegold containing zirconia support material at temperatures above about300° C., the risk that the CO₂ selectivity of the resultant catalystwill be detrimentally affected is reduced.

Exemplary protocols including a calcining step include: a) impregnatingwith palladium followed by calcining followed by impregnating with gold;b) co-impregnating palladium and rhodium followed by calcining followedby impregnating with Au; c) impregnating with palladium followed bycalcining followed by impregnating with rhodium followed by calciningfollowed by impregnating with gold; or d) impregnating with palladiumand rhodium, followed by impregnating with gold, followed bycalcination.

Reducing Step

Another step employed generally herein to at least partially transformany remaining catalytic components from a salt or oxide form to acatalytically active state, such as by a reducing step. Typically thisis done by exposure of salts or oxides to a reducing agent, examples ofwhich include ammonia, carbon monoxide, hydrogen, hydrocarbons, olefins,aldehydes, alcohols, hydrazine, primary amines, carboxylic acids,carboxylic acid salts, carboxylic acid esters and combinations thereof.Hydrogen, ethylene, propylene, alkaline hydrazine and alkalineformaldehyde and combinations thereof are preferred reducing agents withethylene and hydrogen blended with inert gases particularly preferred.Although reduction employing a gaseous environment is preferred, areducing step carried with a liquid environment may also be used (e.g.employing a reducing solution). The temperature selected for thereduction can range from ambient up to about 550° C. Reduction timeswill typically vary from about 1 to about 5 hours.

Since the process used to reduce the catalytic components may influencesthe characteristics of the final catalyst, conditions employed for thereduction may be varied depending on whether high activity, highselectivity or some balance of these properties is desired.

In one embodiment, palladium is contacted to the support material, fixedand reduced before gold is contacted and reduced, as described in U.S.Pat. Nos. 6,486,093, 6,015,769 and related patents, all of which areincorporated by reference.

Exemplary protocols including a reducing step include: a) impregnatingwith palladium followed by optionally calcining followed by impregnatingwith gold followed by reducing; b) co-impregnating with palladium andgold followed by optionally calcining followed by reducing; or c)impregnating with palladium followed by optionally calcining followed byreducing followed by impregnating with gold.

Modifying Step

Usually after the reducing step and before the catalyst is used, amodifying step is desirable. While the catalyst may be used with themodifying step, the step has several beneficial results, includinglengthening the operational life time of the catalyst. The modifyingstep is sometimes called an activating step and may be accomplished inaccordance with conventional practice. Namely, the reduced supportmaterial is contacted with a modifying agent, such as an alkali metalcarboxylate and/or alkali metal hydroxide, prior to use. Conventionalalkali metal carboxylates such as the sodium, potassium, lithium andcesium salts of C₂₋₄ aliphatic carboxylic acids are employed for thispurpose. A preferred activating agent in the production of VA is analkali acetate, with potassium acetate (KOAc) being the most preferred.

The support material may optionally be impregnated with a solution ofthe modifying agent. After drying, the catalyst may contain, forexample, about 10 to about 70, preferably about 20 to about 60 grams ofmodifying agent per liter of catalyst.

Methods of Making Alkenyl Alkanoates

The present invention may be utilized to produce alkenyl alkanoates froman alkene, alkanoic acid and an oxygen containing gas in the presence ofa catalyst. Preferred alkene starting materials contain from two to fourcarbon atoms (e.g. ethylene, propylene and n-butene). Preferred alkanoicacid starting materials used in the process of this invention forproducing alkenyl alkanoates contain from two to four carbon atoms(e.g., acetic, propionic and butyric acid). Preferred products of theprocess are VA, vinyl propionate, vinyl butyrate, and allyl acetate. Themost preferred starting materials are ethylene and acetic acid with theVA being the most preferred product. Thus, the present invention isuseful in the production of olefinically unsaturated carboxylic estersfrom an olefinically unsaturated compound, a carboxylic acid and oxygenin the presence of a catalyst. Although the rest of the specificationdiscusses VA exclusively, it should be understood that the catalysts,method of making the catalysts and production methods are equallyapplicable to other alkenyl alkanoates, and the description is notintended as limiting the application of the invention to VA.

When VA is produced using the catalyst of the present invention, astream of gas, which contains ethylene, oxygen or air, and acetic acidis passed over the catalyst. The composition of the gas stream can bevaried within wide limits, taking in account the zone of flammability ofthe effluent. For example, the molar ratio of ethylene to oxygen can beabout 80:20 to about 98:2, the molar ratio of acetic acid to ethylenecan be about 100:1 to about 1:100, preferably about 10:1 to 1:10, andmost preferably about 1:1 to about 1:8. The gas stream may also containgaseous alkali metal acetate and/or inert gases, such as nitrogen,carbon dioxide and/or saturated hydrocarbons. Reaction temperatureswhich can be used are elevated temperatures, preferably those in therange of about 125-220° C. The pressure employed can be a somewhatreduced pressure, normal pressure or elevated pressure, preferably apressure of up to about 20 atmospheres gauge.

In addition to fixed bed reactors, the methods of producing alkenylalkanoates and the catalyst of the present invention may also besuitably employed in other types of reaction, for example, fluidized bedreactors.

EXAMPLES

The following examples are provided for illustration only and notintended to be limiting. The amounts solvents and reactants areapproximate. The Au/Pd atomic ratio may be converted to the Au/Pd weightratio and vice versa by the following equations: Au/Pd atomicratio=0.54*(Au/Pd weight ratio) and Au/Pd weight ratio=1.85(Au/Pd atomicratio. Reduction may be abbreviated ‘R’ followed by the temperature in °C. at which the reduction was carried out. Likewise, calcination may beabbreviated ‘C’ followed by the temperature in ° C. at which thecalcination was carried out, whereas a drying step may be abbreviated as‘dry’.

The catalyst of examples 1-11 may be prepared as described in theexample and tested according to the following procedure, where catalystfrom Examples 1-7 may be compared to each other and catalyst from 8-11may be compared to each other. Results are provided where available.

The catalysts of the examples were tested for their activity andselectivity to various by-products in the production of vinyl acetate byreaction of ethylene, oxygen and acetic acid. To accomplish this, about60 ml of the catalyst prepared as described were placed in a stainlesssteel basket with the temperature capable of being measured by athermocouple at both the top and bottom of the basket. The basket wasplaced in a Berty continuously stirred tank reactor of the recirculatingtype and was maintained at a temperature which provided about 45% oxygenconversion with an electric heating mantle. A gas mixture of about 50normal liters (measured at N.T.P.) of ethylene, about 10 normal litersof oxygen, about 49 normal liters of nitrogen, about 50 g of aceticacid, and about 4 mg of potassium acetate, was caused to travel underpressure at about 12 atmospheres through the basket, and the catalystwas aged under these reaction conditions for at least 16 hours prior toa two hour run, after which the reaction was terminated. Analysis of theproducts was accomplished by on-line gas chromatographic analysiscombined with off-line liquid product analysis by condensing the productstream at about 10° C. to obtain optimum analysis of the end productscarbon dioxide (CO₂), heavy ends (HE) and ethyl acetate (EtOAc), theresults of which may be used to calculate the percent selectivities (CO₂Selectivity) of these materials for each example. The relative activityof the reaction expressed as an activity factor (Activity) may becomputer calculated using a series of equations that correlates theactivity factor with the catalyst temperature (during the reaction),oxygen conversion, and a series of kinetic parameters for the reactionsthat take place during VA synthesis. More generally, the activity factortypically is inversely related to the temperature required to achieveconstant oxygen conversion.

RHODIUM CATALYST EXAMPLES Example 1

A support material containing palladium and rhodium metal was preparedas follows: The support material in an amount of 250 ml consisting ofSud Chemie KA-160 silica spheres having a nominal diameter of 7 mm., adensity of about 0.569 g/ml, in absorptivity of about 0.568 g H₂O/gsupport, a surface area of about 160 to 175 m²/g, and a pore volume ofabout 0.68 ml/g., was first impregnated by incipient wetness with 82.5ml of an aqueous solution of sodium tetrachloropalladium (II) (Na₂PdCl₄)and rhodium chloride trihydrite (RhCl₃.3H₂O) sufficient to provide about7 grams of elemental palladium and about 0.29 grams of elemental rhodiumper liter of catalyst. The support was shaken in the solution for 5minutes to ensure complete absorption of the solution. The palladium andrhodium were then fixed to the support as palladium (II) and rhodium(III) hydroxides by contacting the treated support by roto-immersion for2.5 hours at approximately 5 rpm with 283 ml of an aqueous sodiumhydroxide solution prepared from 50% w/w NaOH/H₂O in an amount of 120%of that needed to convert the palladium and rhodium to their hydroxides.The solution was drained from the treated support and the support wasthen rinsed with deionized water and dried at 100° C. in a fluid beddrier for 1.2 hours. The support material containing palladium andrhodium hydroxides was then impregnated with an aqueous solution (81 ml)containing 1.24 g Au from NaAuCl₄ and 2.71 g 50% NaOH solution (1.8equivalents with respect to Au) using the incipient wetness method. TheNaOH treated pills were allowed to stand overnight to ensureprecipitation of the Au salt to the insoluble hydroxide. The pills werethoroughly washed with deionized water (˜5 hours) to remove chlorideions and subsequently dried at 100° C. in a fluid bed drier for 1.2hours. The palladium, rhodium, and gold containing support was thencalcined at 400° C. for 2 hours under air and then allowed to naturallycool to room temperature. The palladium, rhodium, and gold were reducedby contacting the support with C₂H₄ (1% in nitrogen) in the vapor phaseat 150° C. for 5 hours. Finally the catalyst was impregnated byincipient wetness with an aqueous solution of 10 g of potassium acetatein 81 ml H₂O and dried in a fluid bed drier at 100° C. for 1.2 hours.

Example 2

A support material utilizing palladium and rhodium hydroxides wasprepared as described in Example 1. The palladium and rhodium containingsupport was then calcined at 400° C. for 2 hours under air and thenallowed to naturally cool to room temperature. The calcined supportmaterial containing palladium and rhodium hydroxides was thenimpregnated with an aqueous solution (81 ml) containing 1.24 g Au fromNaAuCl₄ and 2.71 g 50% NaOH solution (1.8 equivalents with respect toAu) using the incipient wetness method. The NaOH treated pills wereallowed to stand overnight to ensure precipitation of the Au salt to theinsoluble hydroxide. The pills were thoroughly washed with deionizedwater (˜5 hours) to remove chloride ions and subsequently dried at 100°C. in a fluid bed drier for 1.2 hours. The palladium, rhodium, and goldwere then reduced by contacting the support with C₂H₄ (1% in nitrogen)in the vapor phase at 150° C. for 5 hours. Finally the catalyst wasimpregnated by incipient wetness with an aqueous solution of 10 g ofpotassium acetate in 81 ml H₂O and dried in a fluid bed drier at 100° C.for 1.2 hours.

Example 3

A support material containing palladium and rhodium hydroxides wasprepared as described in Example 1. The palladium and rhodium containingsupport was then calcined at 400° C. for 2 hours under air and thenallowed to naturally cool to room temperature. The calcined supportmaterial containing palladium and rhodium hydroxides was then reduced bycontacting the support with C₂H₄ (1% in nitrogen) in the vapor phase at150° C. for 5 hours. The support containing palladium and rhodium metalwas subsequently impregnated with an aqueous solution (81 ml) containing1.24 g Au from NaAuCl₄ and 2.71 g 50% NaOH solution (1.8 equivalentswith respect to Au) using the incipient wetness method. The NaOH treatedpills were allowed to stand overnight to ensure precipitation of the Ausalt to the insoluble hydroxide. The pills were thoroughly washed withdeionized water (˜5 hours) to remove chloride ions and subsequentlydried at 100° C. in a fluid bed drier for 1.2 hours. The palladium,rhodium, and gold were then reduced by contacting the support with C₂H₄(1% in nitrogen) in the vapor phase at 150° C. for 5 hours. Finally thecatalyst was impregnated by incipient wetness with an aqueous solutionof 10 g of potassium acetate in 81 ml H₂O and dried in a fluid bed drierat 100° C. for 1.2 hours.

Example 4

A support material containing palladium and rhodium hydroxides wasprepared as described in Example 1. The palladium and rhodium containingsupport was then calcined at 400° C. for 2 hours under air and thenallowed to naturally cool to room temperature. The calcined supportmaterial containing palladium and rhodium hydroxides was then reduced bycontacting the support with C₂H₄ (1% in nitrogen) in the vapor phase at150° C. for 5 hours. The support containing palladium and rhodium metalwas subsequently impregnated with an aqueous solution (81 ml) containing1.1 g Au from KAuO₂ using the incipient wetness method. The pills weresubsequently dried at 100° C. in a fluid bed drier for 1.2 hours. Thepalladium, rhodium, and gold were then reduced by contacting the supportwith C₂H₄ (1% in nitrogen) in the vapor phase at 150° C. for 5 hours.Finally the catalyst was impregnated by incipient wetness with anaqueous solution of 10 g of potassium acetate in 81 ml H₂O and dried ina fluid bed drier at 100° C. for 1.2 hours.

Example 5

A support material containing palladium and rhodium hydroxides wasprepared as described in Example 1. The palladium and rhodium containingsupport was then calcined at 400° C. for 2 hours under air and thenallowed to naturally cool to room temperature. The calcined supportcontaining palladium and rhodium hydroxides was subsequently impregnatedwith an aqueous solution (81 ml) containing 1.1 g Au from KAuO₂ usingthe incipient wetness method. The pills were then dried at 100° C. in afluid bed drier for 1.2 hours. The palladium, rhodium, and gold werethen reduced by contacting the support with C₂H₄ (1% in nitrogen) in thevapor phase at 150° C. for 5 hours. Finally the catalyst was impregnatedby incipient wetness with an aqueous solution of 10 g of potassiumacetate in 81 ml H₂O and dried in a fluid bed drier at 100° C. for 1.2hours.

Example 6

A support material containing palladium and rhodium hydroxides wasprepared as described in Example 1. The palladium and rhodium containingsupport was then calcined at 400° C. for 2 hours under air and thenallowed to naturally cool to room temperature. The calcined supportmaterial containing palladium and rhodium hydroxides was then reduced bycontacting the support with C₂H₄ (1% in nitrogen) in the vapor phase at150° C. for 5 hours. The support containing palladium and rhodium metalwas subsequently impregnated with an aqueous solution (81 ml) containing1.1 g Au from KAuO₂ and 10 g potassium acetate using the incipientwetness method. The pills were subsequently dried at 100° C. in a fluidbed drier for 1.2 hours.

Example 7 Reference Catalyst

A support material containing palladium metal was prepared as follows:The support material in an amount of 250 ml consisting of Sud ChemieKA-160 silica spheres having a nominal diameter of 7 mm., a density ofabout 0.569 g/ml, in absorptivity of about 0.568 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g., was first impregnated by incipient wetness with 82.5 ml of anaqueous solution of sodium tetrachloropalladium (II) (Na₂PdCl₄)sufficient to provide about 7 grams of elemental palladium per liter ofcatalyst. The support was shaken in the solution for 5 minutes to ensurecomplete absorption of the solution. The palladium was then fixed to thesupport as palladium (II) hydroxides by contacting the treated supportby roto-immersion for 2.5 hours at approximately 5 rpm with 283 ml of anaqueous sodium hydroxide solution prepared from 50% w/w NaOH/H₂O in anamount of 110% of that needed to convert the palladium to its hydroxide.The solution was drained from the treated support and the support wasthen rinsed with deionized water and dried at 100° C. in a fluid beddrier for 1.2 hours. The support material containing palladium hydroxidewas then impregnated with an aqueous solution (81 ml) containing 1.24 gAu from NaAuCl₄ and 2.71 g 50% NaOH solution (1.8 equivalents withrespect to Au) using the incipient wetness method. The NaOH treatedpills were allowed to stand overnight to ensure precipitation of the Ausalt to the insoluble hydroxide. The pills were thoroughly washed withdeionized water (˜5 hours) to remove chloride ions and subsequentlydried at 100° C. in a fluid bed drier for 1.2 hours. The palladium andgold containing support was then reduced by contacting the support withC₂H₄ (1% in nitrogen) in the vapor phase at 150° C. for 5 hours. Finallythe catalyst was impregnated by incipient wetness with an aqueoussolution of 10 g of potassium acetate in 81 ml H₂O and dried in a fluidbed drier at 100° C. for 1.2 hours. Table 1 shows comparison CO₂selectivity and activity for the catalyst of Examples 1 and 7.

TABLE 1 CO₂ Selectivity Activity Example 1 9.89 2.32 Example 7(Reference Catalyst) 11.13 2.36

LAYERED SUPPORT EXAMPLES Example 8

40 g of ZrO₂ (RC-100, supplied by DKK) was calcined at 650° C. for 3 h.Resulting material has a BET surface area 38 m²/g. The material was ballmilled with 120 ml of DI water for 6 h. The sol was mixed with 22.5 g ofthe binder zirconium acetate supplied by DKK (ZA-20) and sprayed onto 55g of spheres of bentonite KA-160 with OD-7.5 mm. Coated beads werecalcined for 3 h at 600° C. Examination under microscope has shownuniform shell formation with thickness of 250 μm.

Example 9

20 g of ZrO₂ (XZ16075, BET surface area 55 m²/g) were impregnated withPd(NO₃)₂ solution (Aldrich) to give Pd loading of 39 mg/g of ZrO2.Impregnated material was dried and calcined at 450° C. for 4 h. Thematerial was ball milled with 60 ml of DI water for 4 h, mixed with 11 gof a binder (ZA-20) and sprayed onto 30 g of bentonite KA-160 spheres.The beads were calcined at 450° C. for 3 h. This procedure results information of a strong uniform shell with 160 μm thickness.

Example 10

The beads from Example 8 were impregnated with solution of potassiumacetate to give loading of 40 mg KOAc/ml of KA-160, dried and calcinedat 300° C. for 4 h. After that the solution, containing 9.4 mM ofPd(from Pd(NH₃)₄(OH)₂ supplied by Heraeus) and 4.7 mM of Au (from a 1 Msolution, Au(OH)₃ “Alfa” dissolved in 1.6 M KOH) was sprayed onto thesebeads. Material was reduced with the mixture: 5% H₂, 95% N₂ at 200° C.for 4 h. The beads were crushed and tested in fix bed micro reactorunder conditions described in the experimental section. CO₂ selectivityof ˜6% at 45% oxygen conversion was achieved.

Example 11 Reference Catalyst

The same catalyst prepared in Example 7 was used as a reference catalysthere. Table 2 shows comparison CO₂ selectivity and activity for thecatalyst of Examples 9-11.

TABLE 2 CO₂ Selectivity Activity Example 9 9.33 2.08 Example 10 9.031.69 Example 11 (Reference Catalyst) 11.13 2.36

Zirconia Support Material and Chloride Free Precursor Examples

The following general procedure was used for this set of examples.Zirconia support material catalysts were made as follows: various shapedcatalyst carriers were crushed and sieved. Zirconia support materialswere supplied by N or Pro (XZ16052 and XZ16075), DKK and MEI. Silicasupport materials were supplied by Degussa and Sud Chemie. The sievefraction of 180-425 um was impregnated (either simultaneously orsequentially with an intermediate drying step at 110° C. and optionallywith an intermediate calcination step) to incipient wetness with a Pdand Au precursor solution, optionally calcined in air, reduced with 5%H₂/N₂ formation gas, post-impregnated with KOAc solution, dried at 100°C. under N₂, and screened in a 8×6 multi channel fixed bed reactor. Asolution of Au(OH)₃ in KOH was used as the Au precursor. Aqueoussolutions of Pd(NH₃)₄(OH)₂, Pd(NH₃)₂(NO₂)₂, Pd(NH₃)₄(NO₃)₂ and Pd(NO₃)₂were used as the Pd precursors.

A silica support material catalyst reference was made as follows: Asupport material containing palladium and rhodium metal was prepared asfollows: The support material in an amount of 250 ml consisting of SudChemie KA-160 silica spheres having a nominal diameter of 7 mm, adensity of about 0.569 g/ml, an absorptivity of about 0.568 g H₂O/gsupport, a surface area of about 160 to 175 m²/g, and a pore volume ofabout 0.68 ml/g., was first impregnated by incipient wetness with 82.5ml of an aqueous solution of sodium tetrachloropalladium (II) (Na₂PdCl₄)sufficient to provide about 7 grams of elemental palladium per liter ofcatalyst. The support was shaken in the solution for 5 minutes to ensurecomplete absorption of the solution. The palladium was then fixed to thesupport as palladium(II) hydroxides by contacting the treated support byroto-immersion for 2.5 hours at approximately 5 rpm with 283 ml of anaqueous sodium hydroxide solution prepared from 50% w/w NaOH/H₂O in anamount of 110% of that needed to convert the palladium to its hydroxide.The solution was drained from the treated support and the support wasthen rinsed with deionized water and dried at 100° C. in a fluid beddrier for 1.2 hours. The support material containing palladium hydroxidewas then impregnated with an aqueous solution (81 ml) containing 1.24 gAu from NaAuCl₄ and 2.71 g 50% NaOH solution (1.8 equivalents withrespect to Au) using the incipient wetness method. The NaOH treatedpills were allowed to stand overnight to ensure precipitation of the Ausalt to the insoluble hydroxide. The pills were thoroughly washed withdeionized water (˜5 hours) to remove chloride ions and subsequentlydried at 100° C. in a fluid bed drier for 1.2 hours. The palladium andgold containing support was then reduced by contacting the support withC₂H₄ (1% in nitrogen) in the vapor phase at 150° C. for 5 hours. Finallythe catalyst was impregnated by incipient wetness with an aqueoussolution of 10 g of potassium acetate in 81 ml H₂O and dried in a fluidbed drier at 100° C. for 1.2 hours. Before testing, the catalyst wascrushed and sieved. The sieved fraction in the size range of 180-425 umwas used.

Catalyst libraries of arrays of 8 rows×6 columns in glass vials weredesigned and a rack of 36 glass vials was mounted on a vortexer andagitated while dispensing metal precursor solutions using Cavro™ liquiddispensing robots. 0.4 ml of support was used for each library element,for the glass vial synthesis as well as loaded to each reactor vessel.

KOAc loading is reported as grams KOAc per liter catalyst volume or asμmol KOAc on 0.4 ml support. For the specification of Au loading, therelative atomic ratio of Au to Pd is reported as Au/Pd. Pd loading isspecified as mg Pd per 0.4 ml support volume (i.e. absolute amount of Pdin reactor vessel).

The screening protocol used a temperature ramp from 145° C. to 165° C.in 5° C. increments, at a fixed space velocity of 175% (with 1.5 mg Pdon 0.4 ml support). 100% space velocity is defined as the followingflows: 5.75 sccm of Nitrogen, 0.94 sccm of Oxygen, 5.94 sccm ofEthylene, and 5.38 microliters per minute of Acetic Acid through each ofthe 48 catalyst vessels (all of which had an inner diameter ofapproximately 4 mm). CO₂ selectivity was plotted versus oxygenconversion, a linear fit performed, and the calculated (interpolated inmost cases) CO₂ selectivity at 45% oxygen conversion reported in theperformance summary tables below. The temperature at 45% oxygenconversion calculated from the T ramp (linear fits of CO₂ selectivityand oxygen conversion versus reaction temperature is also reported). Thelower this calculated temperature the higher the activity of thecatalyst. The space time yield (STY; g VA produced per ml catalystvolume per h) at 45% oxygen conversion is a measure of the productivityof the catalyst.

Example 12

400 ul of ZrO₂ carriers XZ16075 (55 m²/g as supplied) and XZ16052(precalcined at 650° C./2 h to lower the surface area to 42 m²/g) wereimpregnated with 3 different Pd solutions to incipient wetness, dried at110° C. for 5 h, impregnated with KAuO₂ (0.97M Au stock solution) toincipient wetness, dried at 110° C. for 5 h, reduced at 350° C. for 4 hin 5% H₂/N₂ formation gas, post-impregnated with KOAc and dried at 110°C. for 5 h. The Pd/Au/ZrO₂ samples (shells) were then diluted 1/9.3 withKA160 diluter (preloaded with 40 g/l KOAc), i.e. 43 ul Pd/Au/ZrO₂ shelland 357 ul diluter (400 ul total fixed bed volume) were charged to thereactor vessels. The Pd loading was 14 mg Pd in 400 ul ZrO2 shell (or14*43/400=14/9.3=1.5 mg Pd in reactor vessel for all library elements.The Pd precursors were Pd(NH₃)₂(NO₂)₂ in columns 1 and 4, Pd(NH₃)₄(OH)₂in columns 2 and 5, Pd(NH₃)₄(NO₃)₂ in columns 3 and 6. Au/Pd=0.3 in row2 and row 5, Au/Pd=0.6 in row 3, Au/Pd=0.9 in row 4, row 6 and row 7.The KOAc loading was 114 umol in rows 2, 3, 5 and 147 umol in rows 4, 6,7. The silica reference catalyst was loaded into Row 1. The library wasscreened using the T ramp screening protocol at fixed SV. Screeningresults are summarized in Table 3

TABLE 3 CO₂ Selectivity Temp at STY Cl Precursors on SiO₂ 7.37 156.6 729Pd(NH₄)₂(OH)₂ on ZrO₂ 5.79 152.4 787 Pd(NH₃)₄(NO₃)₂ on ZrO₂ 5.90 152.3783 Pd(NH₃)₂(NO₂)₂ on ZrO₂ 5.57 150.7 795 *Data shown is taken fromaverage of two Au/Pd atomic ratios (namely 0.3 and 0.6) and twodifferent ZrO₂ supports.

Example 13

400 ul of ZrO₂ carriers XZ16075 (55 m²/g as supplied) and XZ16052(precalcined at 650° C./2 h to lower the surface area to 42 m²/g) wereimpregnated with Pd(NH₃)₄(OH)₂ (1.117M Pd stock solution) to incipientwetness, calcined at 350° C. for 4 h in air, impregnated with KAuO₂(0.97M Au stock solution) to incipient wetness, dried at 110° C. for 5h, reduced at 350° C. for 4 h in 5% H₂/N₂ formation gas,post-impregnated with KOAc and dried at 110° C. for 5 h. The Pd/Au/ZrO₂samples (shells) were then diluted 1/12 with KA160 diluter (preloadedwith 40 g/l KOAc), i.e. 33.3 ul Pd/Au/ZrO₂ catalyst and 366.7 ul diluter(400 ul total fixed bed volume) were charged to the reactor vessels. Thelibrary design and library element compositions were as follows: ZrO₂XZ16075 in columns 1-3 (left half of library) and ZrO2 XZ16052 (650° C.)in columns 4-6 (right half of library). The Pd loading was 18 mg Pd in400 ul ZrO₂ shell (or 18*33/400=18/12 mg Pd in reactor vessel) in cellG2, column 3 (cells B3-G3), cell G5, column 6 (cells B6-G6); 10 mg Pd in400 ul ZrO₂ shell (or 10*33/400=10/12 mg Pd in reactor vessel) in column1 (cells Al-G1) and column 4 (cells A4-G4); 14 mg Pd in 400 ul ZrO₂shell (or 14*33/400=14/12 mg Pd in reactor vessel) in column 2 (cellsB2-F2) and column 5 (cells B5-F5). Au/Pd=0.3 in row 2 and row 5,Au/Pd=0.5 in row 3 and row 6, Au/Pd=0.7 in row 4 and row 7 (except cellsA1, A4, G2, G5 where Au/Pd was 0.3). The KOAc loading was 114 umol(except cells D3, G3, D6, G6 where KOAc loading was 147 umol). Thesilica reference catalyst was loaded into Row 1. The library wasscreened using the T ramp screening protocol at fixed SV. Screeningresults are summarized in Table 4.

TABLE 4 CO₂ Selectivity Temp at 45% Conv STY Au/Pd Atomic Ratio 0.3 0.50.7 0.3 0.5 0.7 0.3 0.5 0.7 Cl Precursors on SiO₂ 6.98 — — 154.8 — —742.8 — — ZrO₂: XZ16052 6.06 5.31 5.38 153.7 152.3 154.9 776.8 806.0803.0 ZrO₂: XZ16075 6.18 5.62 5.71 147.5 151.0 154.4 773.8 791.6 790.3

Example 14

ZrO2 carrier (supplied by N or Pro, XZ16075, sieve fraction 180-425 um,density 1.15 g/ml, pore volume 475 ul/g, BET surface area 55 m2/g) wasimpregnated with Pd(NO₃)₂ precursor solution to incipient wetness, driedat 110° C., calcined at 250° C. (columns 1-2), 350° C. (columns 3-4),450° C. (columns 5-6) in air, impregnated with KAuO₂ solution (preparedby dissolution of Au(OH)₃ in KOH), dried at 110° C., reduced with 5%H₂/N₂ formation gas at 350° C. for 4 h, and post-impregnated with KOAcsolution. The library has a KOAc gradient from 25 to 50 μl in row 2 torow 7. The Pd loading amounts to 1.5 mg Pd on 0.4 ml support. Twodifferent Au loadings were chosen (Au/Pd=0.5 in columns 1, 3, 5 andAu/Pd=0.7 in columns 2, 4, 6). The silica reference catalyst was loadedin row 1. The library was screened using the T ramp screening protocolin MCFB48 VA reactor at fixed SV. Screening results are summarized inTable 5.

TABLE 5 CO₂ Selectivity Temp at 45% Conv STY Cl Precursors on SiO₂ 7.21154.7 734 Pd(NO3)2 on ZrO2 6.10 145.3 775 *Data shown is taken fromaverage of two Au/Pd atomic ratios (namely 0.5 and 0.7) at 40 g/L KOAc,calcination at 450° C., and reduction at 350° C.

Example 15

ZrO₂ carrier (supplied by N or Pro, XZ16075, sieve fraction 180-425 um,density 1.15 g/ml, pore volume 575 ul/g, BET surface area 55 m2/g) wasimpregnated with Pd(NO₃)₂ precursor solution to incipient wetness, driedat 110° C., calcined at 450° C. in air, impregnated with KAuO₂ solution(prepared by dissolution of Au(OH)₃ in KOH), dried at 110° C., reducedwith 5% H₂/N₂ formation gas at 200° C. (columns 1-2), 300° C. (columns3-4), or 400° C. (columns 5-6), and post-impregnated with KOAc solution.The library has a KOAc gradient from 15 to 40 g/l in row 2 to row 7. ThePd loading amounts to 1.5 mg Pd on 0.4 ml support. Two different Auloadings were chosen (Au/Pd=0.5 in columns 1, 3, 5 and Au/Pd=0.7 incolumns 2, 4, 6). The silica reference catalyst was loaded in row 1. Thelibrary was screened in MCFB48 VA reactor using the T ramp screeningprotocol at fixed SV. Screening results are summarized in Table 6.

TABLE 6 CO₂ Selectivity Temp at 45% Conv STY Cl Precursors on SiO₂ 7.11154.2 738 Pd(NO3)2 on ZrO2 5.51 145.4 797 *Data shown is taken fromaverage of two Au/Pd atomic ratios (namely 0.5 and 0.7) at 40 g/L KOAc,calcination at 450° C., and reduction at 400° C.

It will be further appreciated that functions or structures of aplurality of components or steps may be combined into a single componentor step, or the functions or structures of one step or component may besplit among plural steps or components. The present inventioncontemplates all of these combinations. Unless stated otherwise,dimensions and geometries of the various structures depicted herein arenot intended to be restrictive of the invention, and other dimensions orgeometries are possible. Plural structural components or steps can beprovided by a single integrated structure or step. Alternatively, asingle integrated structure or step might be divided into separateplural components or steps. In addition, while a feature of the presentinvention may have been described in the context of only one of theillustrated embodiments, such feature may be combined with one or moreother features of other embodiments, for any given application. It willalso be appreciated from the above that the fabrication of the uniquestructures herein and the operation thereof also constitute methods inaccordance with the present invention.

The explanations and illustrations presented herein are intended toacquaint others skilled in the art with the invention, its principles,and its practical application. Those skilled in the art may adapt andapply the invention in its numerous forms, as may be best suited to therequirements of a particular use. Accordingly, the specific embodimentsof the present invention as set forth are not intended as beingexhaustive or limiting of the invention. The scope of the inventionshould, therefore, be determined not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. The disclosures of all articles and references,including patent applications and publications, are incorporated byreference for all purposes.

1. A method of producing a catalyst or pre-catalyst suitable forassisting in the production of alkenyl alkanoates, comprising: layeringa first support material and a surfactant or bonding agent on to asecond support material to produce a particulate, layered supportmaterial having an outer layer and an inner layer, wherein catalyticcomponents of palladium, gold or combinations thereof are contained inthe outer layer of the layered support material.
 2. The method of claim1 wherein the layering step comprises slurry coating the first supportmaterial and the surfactant or bonding agent on to the second supportmaterial.
 3. The method of claim 2 wherein layering step comprises washcoating or spray coating the first support material and the surfactantor bonding agent on to the second support material.
 4. The method ofclaim 1 wherein the bonding agent is selected from organic and inorganicbonding agents.
 5. The method of claim 4 wherein the bonding agent is aninorganic bonding agent.
 6. The method of claim 5 wherein the bondingagent is selected from a alumina bonding agent, a silica bonding agent,a zirconia bonding agent or combinations there of.
 7. The method ofclaim 1 further comprising contacting the catalytic components to thefirst support material before the layering step.
 8. The method of claim1 wherein the inner layer is substantially free of catalytic components.9. The method of claim 8 wherein the second support material isnon-porous.
 10. The method of claim 1 wherein the first support materialis zirconia.
 11. The method of claim 1 wherein the particulate layeredsupport material has a size in the range of between about 4 and 8 mm.12. A composition for catalyzing the production of an alkenylalkanoates, comprising: a particulate, layered support materialcomprising at least an outer layer comprising a first support material,a surfactant or bonding agent and an inner layer comprising a secondsupport material wherein the outer layer comprises at least palladium incombination with gold contacted thereon to form a pre-catalyst orcatalyst, wherein the inner layer is substantially free of palladium andgold.
 13. The composition of claim 12 wherein the outer layer is aslurry coated layer.
 14. The composition of claim 13 wherein the outerlayer is a wash coated or spray coated layer.
 15. The composition ofclaim 12 wherein the bonding agent is part of the slurry coated layer.16. The composition of claim 12 wherein the bonding agent is aninorganic bonding agent.
 17. The composition of claim 16 wherein thebonding agent is selected from a alumina bonding agent, a silica bondingagent, a zirconia bonding agent or combinations there of.
 18. Thecomposition of claim 13 wherein the particulate layered support materialhas a size in the range of between about 4 and 8 mm
 19. The compositionof claim 13 wherein the outer layer comprises zirconia.
 20. Thecomposition of claim 12 wherein the pre-catalyst or catalyst comprisesbetween about 1 to about 10 grams of palladium, and about 0.5 to about10 grams of gold per liter of catalyst, with the amount of gold beingfrom about 10 to about 125 wt % based on the weight of palladium.